Acoustic device



Sept. 27, 1932. BENECKE 1,879,042

ACOUSTIC DEVICE Filed April 8, 1931 Fig. 4.

Inventor. Heinrich Be'necke, bg m His Abborneg.

Patented Sept. 27, 1932 HEINRICH BENECKE, OF BERLIN-PANKOW,

GERMANY, assreivon 'ro GENERAL ELEC- TBIC COMPANY, A CORPORATION OF NEW YORK ACOUSTIC DEVICE Application filed April 8, 1981, Serial No.

. My invention relates to acoustic devices such as electrodynamic loudspeakers, particularly tomeans for centering the diaphragms of such acoustic devices with relation to the diaphragm driving unit, and has for its principal object the provision of an improved centering device whereby free vibration of the diaphragm is insured at lowest frequencies and at greatest amplitudes without danger of 0 failure of the centering means.

- It has been theusual practice in the construction of electrodynamic loudspeakers to support the cone-shaped diaphragm at its upper, or outer end in such a manner as to m insure free movement of the cone. In order that the body of the diaphragm may be maintained in a position of equilibrium by a small elastic directional force tending to return the diaphragm to a neutral position, while insuring at the same time that the vibration of the diaphragm shall occur only in a direction parallel to the cone axis of thediaphragm, it has also been the usual practice to provide the lower, or inner end of the diaphragm with an inside or outside centering means known as a centering disk or spidery Since it is desirable that the cone diaphragm thus supported shall possess a low natural period of vibration, it is necessary :u) that the centering means be characterized by only a small flexural elasticity. Therefore, for this purpose thin circular disks of paper or the like have been utilized, these disks being secured at their center to the drivin unit and at their outer edge to the lower e ge of the truncated cone diaphragm.

Such a centering device, however, because ofits slight mechanical strength involves the drawback that in case of diaphragm vibra tions of low pitch and large amplitude the diameter disk mounted inside the lower end of the cone, it is then not possible to maintain the natural period of vibration of the'small 528,648, and in Germany April 25, 1980.

mass diaphragm sufiiciently low to insure that the reproduction of-v tones of low frequency shall not be impaired.

On the other hand, the use of fabric or cloth I I such as silk or the like as the material for the centering disk or spider is not satisfactory. While these materials possess the requisite tensile strength to support the diaphragm, yet because of their low flexural elasticity the elastic directional force which they exert upon the mass of the diaphragm is too low.

In accordance with my invention these difficulties are avoided by the provision of a centering device for the diaphragms of electrodynamic loudspeakers which consists of different materials possessing such properties that at the same time the required elasticity and strength in the centering deviceare provided. This end is attained by the combination of two layers of different material, one of the materials having the elasticity required in the resulting composite centering device and the other material having the tensile strength required in this composite centering device.

A composite. centering device formed by a combination of cellon and of oil-impregnated silk securedthereto by pasting has proved especially well adapted to the purpose described, although other suitable combinations may be used, particularly paper and oil-impregnated silk, or paper and ordinary silk, 'or the like.

One of the layers, preferably the layer characterized by the hlgher elasticity, may be provided with the openings orv cut-outs usual in diaphragm centering disks, the surface ofthe other layer remaining unbroken, or both layers may be provided with such openings or cut-outs, preferably of similar kind in the two layers.

My invention will be better understood from the following description when considered in connection with the accompanying drawing and its scope will'be pointedout in the appended claims;

. Referring to the drawing, Fig. 1 illustrates a diaphragm centering disk embodying my invention; Fig. 2 illustrates a modification of the embodiment shown in Fig. 1; Fig.

3 is a cross section of the centering disk; and Fig. a illustrates a loudspeaker device in which a diaphragm centering disk in accordance with my invention is incorporated.

In the embodiments of the invention illustrated in Figs. 1 to 3 a centering disk 10 is composed of two thin layers 11, 12. The layer ll is a thin sheet of elastic material preferably cellon, and the layer 12 is a sheet of material of relatively high tensile strength, preferably oil-impregnated silk, which is secured to the layer 11 in a suitable manner as by a pasting or cementing process. In the form of the invention shown in Fig. 1 the elastic layer 11 is shown as provided with openings or cut-outs 13, the surface of the layer 12 however remaining unbroken. In the form of the invention shown in Fig. 2 both layers are provided with openings or cut-outs.

In Fig. 4 is illustrated an elect-rodynamic loudspeaker 14 comprising a conical diaphragm 15. The diaphragm is provided at its lower or smaller end with an actuating coil 16 and with a centering disk 10. In accordance with my invention the disk 10 is a composite structure built up, as described in connection with Figs. 1 to 3, of a thin top layer or outer layer 11 provided with openings or cut-outs 13 and composed of elastic material, which in the form of the invention shown in Fig. 4 is cellon, and of a lower or inner layer 12 of a. material characterized bv relatively great tensile strength as oiled silk, this secondlayer being pasted or cemented to the top layer to form therewith a unitary structure. The composite disk 10 resulting from the combination of the two portions 11 and 12 which have diflerent characteristics is fastened centrally in the usual manner as by a screw 17 to the magnet core 18, but peripherally the disk is movable when the cone 15 to which the outer edge of the disk is attached is caused to vibrate by the forces acting on the actuating coil 16.

In operation, the outer thin elastic layer 11 provides the necessary elastic restoring force exerted upon the mass of the vibrating diaphragm, this force however not being of suflicient magnitude to prevent the free vibration of the diaphragm even at a predetermined low natural period of vibration thereof. At the same time the inner layer 12, which while not possessing sutiic-ient elasticity to exert a required restoring force upon the diaphragm is characterized by a. tensile strength large in comparison with that of the elastic layer 11, prevents tearing or rupturing of the composite centering disk or spider 10 during all conditions of vibration of the diaphragm including vibrations of the maximum amplitude.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. In an acoustic device comprising a diaphragm, a centering device for said diaphragm comprising two layers, one of said layers being composed of an elastic material, the other of said layers being composed of a material having less elasticity but greater tensile strength than said one of said layers.

2. In an acoustic device comprising a diaphragm, a composite centering device for said diaphragm having two layers respectively composed of paper and of silk.

3. In an acoustic device comprising a diaphragm, a composite centering device for said diaphragm having two layers respectively composed of paper and of oiled silk.

4. In an acoustic device comprising a diaphragm, a composite centering device for said diaphragm, said centering device comprising a layer of cellon and a layer of oiled silk secured thereto.

5. In an acoustic device comprising a diaphragm adapted to vibrate over a predetermined range of frequencies and between predetermined limits of amplitude, a centering device for said diaphragm comprising two layers of material, said materials having such properties that a predetermined degree of elasticity and a predetermined tensile strength are provided in said centering device.

6. In an electrodynamic loudspeaker comprising a cone diaphragm, acomposite centering device for said diaphragm adapted to exert on said diaphragm an elastic force tending to return said diaphragm to a position of equilibrium but insufiicient to prevent free vibration of said diaphragm at the lowest frequency of vibration thereof, and adapted to insure the vibration of said diaphragm in a direction parallel to the axis of said cone at the greatest amplitude of vibration of said diaphragm.

7 In an electrodynamic loudspeaker comprising a cone diaphragm, a centering disk for said diaphragm, a portion of said disk being composed of an elastic material to exert a small directional force on said diaphragm tending to return said diaphragm to a position of equilibrium, and another portion of said disk being composed of a material of relatively high tensile strength to insure the vibration of said diaphragm in a direction parallel to the axis of said cone.

In witness whereof I have hereunto set my hand.

HEINRICH BENECKE. 

